willowherbPronunciation: /ˈwɪləʊhəːb/Definition of willowherb noun a plant of temperate regions that typically has willow-like leaves and pink or pale purple flowers. Epilobium and related genera, family Onagraceae: many species, including the common great hairy willowherb (E. hirsutum) of Eurasia, and the rosebay willowherb in other Oxford dictionaries Definition of willowherb in the US English dictionary